Waco police Sgt. W. Patrick Swanton said an uninvited group appeared for the meeting of a loose confederation of biker gangs Sunday at a restaurant.

One man was injured when a vehicle rolled over his foot. That caused a dispute that continued inside the restaurant, where fighting and then shooting began, before the melee spilled back outside, Swanton said.

Authorities offered few details. It was not clear which gang was responsible for running over the biker's foot, or which gang the aggrieved biker belonged to.

When the shootout was over, nine people were dead and 18 wounded.

About 50 weapons were confiscated, mostly knives and firearms, and Swanton said more than 100 weapons may be found once authorities are done analyzing the crime scene at the Twin Peaks restaurant, which is part of a national chain that features waitresses in revealing uniforms.

Preliminary autopsy results showed all nine of the dead were killed by gunshots. Many were hit in the head, neck, chest or torso. Most of the men were in their 40s, but they ranged in age from 27 to 65, according to reports released by a McLennan County justice of the peace.

Police have acknowledged firing on armed bikers, but it was unclear how many of the dead were shot by gang members and how many were shot by officers.

Of the injured, seven remain hospitalized. Swanton, who has been virtually the sole source of law enforcement information on the fight, described their conditions as stable.

He said the investigation is being hampered by witnesses who "are not being honest with us."

Police are concerned that the brawl will invite retaliation and more violence, Swanton said.

"We would encourage them to try to be a little peaceful and let the bloodshed stop," he said.

Authorities warned weeks ago of growing animosity between rival motorcycle gangs, a feud that erupted into violence at the restaurant, which had drawn a large lunchtime crowd to a busy Waco shopping complex along Interstate 35.

In a memo dated May 1, the Texas Department of Public Safety cautioned authorities about increasing violence between the Bandidos and the Cossacks, Dallas TV station WFAA reported Monday.

McLennan County Sheriff Parnell McNamara has said all nine of those killed were part of those two groups. About 170 bikers have been charged with engaging in organized crime. Swanton said more arrests are likely.

McLennan County Justice of the Peace W.H. Peterson set bond at $1 million for each suspect. He defended the high amount, citing the violence that quickly unfolded in a shopping market busy with a lunchtime crowd.

The DPS Joint Information Center bulletin said the tension could stem from Cossacks refusing to pay Bandidos dues for operating in Texas and for wearing a patch on their vest that claimed Texas as their turf without the Bandidos' approval.

"Traditionally, the Bandidos have been the dominant motorcycle club in Texas, and no other club is allowed to wear the Texas bar without their consent," the bulletin said, according to WFAA.

The bulletin said the FBI had received information that the Bandidos had discussed "going to war with Cossacks." It also outlined several recent incidents between the two groups, including one instance in March when about 10 Cossacks forced a Bandido to pull over along Interstate 35 near Waco and attacked him with "chains, batons and metal pipes before stealing his motorcycle," WFAA reported.

That same day, a group of Bandidos confronted a Cossack member fueling up at a truck stop in Palo Pinto County, west of Fort Worth, the bulletin said. When the Cossack member refused to remove the Texas patch from his vest, the Bandidos hit him in the head with a hammer and stole it.

There are other documented instances of violence between the groups.

Last March, two members of the Bandidos were indicted in connection with the stabbing of two Cossacks at an Abilene steakhouse in March 2014.

And in December, three Bandidos were arrested for a shooting at a Fort Worth motorcycle bar that left one dead and two others wounded. Fort Worth police said the victims were known members of a criminal motorcycle gang.

The Bandidos "constitute a growing criminal threat," the Justice Department said in a report on outlaw motorcycle gangs. The report said the Bandidos are involved in transporting and distributing cocaine and marijuana and in the production and distribution of methamphetamine.

The Texas Department of Public Safety declined to release the bulletin to The Associated Press.

Five gangs from across Texas had gathered at Twin Peaks in part to settle differences over turf, Swanton has said.

The Confederation of Clubs, a network of motorcycle groups, had scheduled a regional meeting at the restaurant, according to their website.

Police and the restaurant operators were aware of Sunday's meeting in advance, and 18 Waco officers in addition to state troopers were outside the restaurant when the fight began, Swanton said.